In application wherein it is necessary to selectively engage a control mechanism with a manual actuating device, one type of device used in the art is a single split nut device in which a half-nut is moved into engagement with a manually rotated screw to effect manual actuation of the control mechanism. One disadvantage of such a device is that excessive bearing stresses can be applied to the rotating screw, which can result in shearing of the nut threads or disengagement due to stripping of the threads. Also, in the prior art mechanism, nut separation forces act on the operating rod which moves the nut into engagement with the screw. As a result of these forces, the operating rod and the rotating screw must be sized accordingly.
Because of the foregoing, it has become desirable to develop an improved locking mechanism for engaging a rotary screw type actuator.